Thread Content
1. When designing the foundations for mechanical pump equipment, the following information should be obtained: (1) The model, speed, power, specifications, and dimensional drawings of the mechanical pump equipment； (2) Machine weight and center of gravity position, or mass distribution diagram of the compressor, motor, and auxiliary equipment ； (3) Basic template diagram, design elevation of the foundation top surface, thickness of the secondary grouting layer, location and specifications (or dimensions) of the anchor bolts (or anchor bolt holes) ； (4) Coordinate position of the equipment foundation in the production unit ； (5) Engineering geological and hydrogeological survey data of the construction site. 2. Requirements for the foundation: (1) The foundation should rest on the old soil layer ； (2) For the foundations of pump equipment with a power of less than 100 KW, when no special requirements are imposed regarding settlement, they can be installed on backfilled soil that has been compacted in layers; the compaction coefficient of such soil should not be less than 0.93 ； (3) The top surface of the foundation should be at least 200 mm above the ground level; its burial depth should be at least 0.8 m, and also not less than the freezing depth. In southern regions, the burial depth should be below the topsoil layer, i.e., 0.5 m ； 3. Requirements for the foundation: (1) The dimensions of the foundation slab should be determined based on the following three criteria: • The mass of the foundation should be 3 to 5 times greater than the mass of the machine ； • P ≤ (0.5–0.7)f, where P is the design average static pressure at the base surface, in kPa ； f—design value of foundation bearing capacity, kPa ； • The overall centroid of the base set and the centroid of the base surface should lie on the same vertical line, with their relative eccentricity not exceeding 3% ； (2) The concrete grade for the foundation is C20, while that for the cushion layer is C10 ； (3) When the volume of the basic concrete is less than 20 m³, surface structural reinforcement may not be provided ； When the concrete volume is 20~40 m3, a steel reinforcement mesh with a diameter of 10 mm and a spacing of 200 mm should be installed on the top surface of the foundation ； When the concrete volume is greater than 40 m3, rebar mesh with a diameter of 10–14 mm and a spacing of 200–300 mm should also be installed around the foundation as well as on its top and bottom surfaces ； The cantilevered portion of the base slab shall be provided with reinforcement on the upper and lower sides based on strength calculations; when the cantilever length of the slab is less than the thickness of the floor, no reinforcement is required ； (4) The secondary pouring layer on the top surface of the foundation should have a thickness of 30–50 mm. Fine aggregate concrete should be used for this layer, and its strength grade should be one level higher than that of the foundation concrete. When the thickness is less than 30 mm, 1:2 cement mortar can be used ； The exposed parts of the foundation are plastered with 1:2 cement mortar ； (5) Self-made anchor bolts should preferably have a straight hook shape, and the length of the straight hook section shall not be less than 4d (where d is the diameter of the anchor bolt) ； The embedment depth L shall not be less than 20 times the diameter; for anchor plate-equipped foot bolts, it shall not be less than 15 times the diameter. Structural bolts are not subject to this restriction, but the embedment depth shall not be less than 300 mm ； The embedding method should involve the use of pre-drilled holes; the distance from the bottom of these holes to the base surface of the foundation must not be less than 100 mm ； The distance from the bottom of the anchor bolt to the bottom of the pre-drilled hole must not be less than 50 mm; the distance from the edge of the pre-drilled hole to the edge of the foundation must not be less than 100 mm ； When embedding bolts: it should be no less than 100 mm when φ≤20, and no less than 150 mm when φ＞20. When the requirements are not met, it is advisable to use rebar mesh with a diameter of 6–8 mm and a spacing of 100–150 mm ； The reserved holes should be filled with fine-grained concrete of grade C25, or with concrete of a grade one higher than that of the foundation ； When the side length of a rectangular foundation or the perimeter of a circular foundation exceeds 40 m, a post-cast strip should be installed; its width is 50 cm, and the rebar is not cut. One month after the pouring of the base slab, it should be poured with concrete of a higher grade than that of the original foundation, along with micro-expansive agents added to it ； The foundation concrete should be poured in one go, without leaving any construction joints. When construction requirements dictate the need to leave construction joints, the structural and operational specifications for such joints must be strictly followed. Equipment can be installed only when the concrete strength reaches over 70%. 4. Power calculation for centrifugal pumps: (1) When the standard value of foundation bearing capacity is not less than 80 kPa, the motor power is not more than 560 kW, and the mass of the centrifugal pump’s foundation is not less than three times the mass of the machine itself, then a power calculation is not necessary ； (2) When dynamic calculations are required for the foundation, the permissible amplitude of the foundation shall comply with the provisions regarding the permissible amplitude of foundations as specified in the table below ； Machine operating speed n (r/min) (mm): 1000 ≥ n > 750 → 0.10; 750 > n ≥ 500 → 0.15; n < 500 → 0.20. (When n > 1000 r/min, the allowable amplitude can be determined according to the manufacturer’s specifications, or it can be set at 0.1 mm.) (3) The disturbance value of the centrifugal pump is calculated using the formula: Pn = mew², where: • Pn – the disturbance value of the centrifugal pump (N) ； • e—Eccentricity of the centrifugal pump (m) ； • w—circular frequency of machine disturbance (1/s), w=0.105n ； • m—mass of the rotating part of the motor (kg). II. Pump Foundation Design 1. General Requirements (1) The design of the pump foundation must be safe and stable, with accurate elevation and dimensions, to ensure stable operation of the pump as well as ease of installation and maintenance. (2) In accordance with the provisions of GB/T50265-97 \"Code for Design of Pumping Stations\": for vertical axial flow pump units with a single-unit power of 160 kW or less, and horizontal centrifugal pump units with a single-unit power of 500 kW or less, it is not necessary to perform dynamic calculations for their pump foundations. Conversely, calculations must be carried out, especially for the pump foundations that are integrated with the structure of the pump house. 2. Key points for the foundation design of horizontal centrifugal pumps (1) Foundation type: It can be divided into separate-type and integral-type based on whether it is connected to the pump house structure. Above-ground pump houses should preferably use separate foundations, while underground or semi-underground pump houses generally use integral foundations that are integrated with the reinforced concrete base slab; the integral foundation is part of the structural design of the pump house. (2) Generally, when the power is below 100 kW, the water pump and motor come with a base, allowing them to be installed directly on the foundation ； For capacities over 100kw, there is no chassis, and the base surface must be padded with steel plates or section bars. (3) Due to the frequent updates and changes in water pumps and motor equipment, as well as the fact that product specifications vary among different manufacturers. Therefore, during the design of construction drawings, it is necessary to obtain materials such as the product technical specifications from the manufacturer; before pouring the foundation, it is advisable to verify the dimensions according to those of the actual equipment. (4) For the foundations of separate medium and small-sized water pumps, design can be carried out with reference to the following empirical data ； The monolithic foundation can be adjusted as appropriate depending on the circumstances, taking into account the structural design of the pump house. • The base material is usually concrete with a strength of not less than C20 ； Reserve screw holes, and after the anchor bolts are inserted, fill them and consolidate them with fine solid concrete of grade C25 or higher. • The length of the anchor bolts embedded in the foundation should be no less than 20 times the diameter of the bolts (l≥20d), while the length of the bolt shanks is 4d ； The depth of the pre-drilled screw hole should be 3–5 cm greater than the total length of the bolt that is to be inserted. • Horizontal water pumps generally have a block foundation, and their dimensions are usually determined based on the data provided for the installation dimensions of the selected pump and motor; if such data is not available, the following figures can be used as a reference. A. For small water pumps with a base: the foundation length L = base length L1 + (0.20~0.30) (m). The base width B = the spacing between the screw holes on the base (in the width direction) + B1 + 0.30 (m). The base height H = the length L2 of the base foot screws + (0.10~0.15) (m). B. For large and medium-sized water pumps without a base: the foundation length L = the distance L1 between the outermost screw holes of the water pump and the motor + (0.40~0.60) (m), and it must be longer than the total length of the motor. The base width B = the distance between the outermost screw holes of the water pump and the motor (taking the larger value), plus (0.40~0.60) (m). The base height H = the length L2 of the base foot screws + (0.10~0.15) (m). C. Foundation height and weight: The foundation weight is >2.5–4.5 times the weight of the unit (pump and motor). The base height should be no less than 500-700 mm ； The base top surface should be 100–200 mm above the indoor floor level, with 200 mm being the typical value. D. Reserved screw holes: When the diameter of the bolt d is ≥ 40 mm, the center distance between the screw holes is 300 mm from the edge of the foundation. When the d-bolt is < 40 mm, the center distance between the screw holes and the edge of the foundation should be > 150–200 mm; however, the distance between the edge of the foundation’s screw holes and the foundation’s edge must not be less than 100–150 mm. The size of the screw holes also needs to take into account the length of the screw fork tail, as well as the concrete filling after the anchor bolts are embedded, which is required under strict construction conditions. The size of the screw holes is generally square openings ranging from 80–200 mm, such as 100 mm×100 mm or 150 mm×150 mm square openings ； Large water pumps are ≥200×200mm. E. For pumps with a motor power of 50 kW or less, expansion bolts can be used for fixation during design; the other requirements are the same as those specified above.